This invention relates to reciprocating slat-type conveyors, and more particularly to a double-sealed, bearingless, reciprocating slat-type conveyor in which the longitudinal edges of the slats are supported by guide trough subdecks.
Reciprocating slat-type conveyors (also referred to as “conveyor systems,” “live floor conveyors,” “reciprocating slat conveyors,” or “conveyors”) generally include a plurality of elongated slats (also referred to as “conveyor slats,” “floor slats,” or “deck slats”). The conveyors are generally used in the load-holding compartment of load transport vehicles (e.g. a mobile cargo trailer, bed of a truck (truck bed), rear portion of a semi-trailer, or container portion of a van-truck). The slats are arranged side-by-side to form the floor of the load-holding compartment so that they extend longitudinally to the framework of the load-holding compartment. A “load” may be, for example, grain, fertilizer, soil, sand, shredded documents, chipped wood, sawdust, garbage, or any particulate matter.
The slats are generally grouped such that one group of slats (a group generally includes at least three slats although it is to be understood that each group may include any desired number in excess of two) moves simultaneously in one direction (the “load-conveying direction”) and then returns one slat at a time (in the “retraction direction”) to the beginning position. This operation results in a step-wise advance of the load positioned on the floor followed by a retraction of the slats without moving the load.
Early live floor conveyors used essentially flat reciprocating slats, such as those described in U.S. Pat. Nos. 3,534,875 and 4,143,760 (which are herein incorporated-by-reference in their entirety). These flat slats rested directly on transverse frame beams and guide beams. This configuration proved problematic because friction between the slats and the beams resulted in great amounts of power lost to friction and the slats not moving smoothly on the beams. This was particularly true when the slats became wet and/or worn.
To alleviate these problems, the industry began using anti-friction bearings between the slats and the beams. This is shown in the pervasive use of bearings in live floor conveyors including, but not limited to those shown in U.S. Pat. Nos. 4,144,963, 4,184,587, 4,611,708, 4,856,645, 5,088,595, 5,165,525, 5,263,573, 5,267,641, 5,301,798, 5,325,957, 5,335,778, 5,547,067, 5,560,472, 5,664,663, 5,727,672, 6,257,396, 6,513,648, 6,651,806, 6,763,933, and 7,152,729 and in U.S. Publication No. 2008/0277246. These references are herein incorporated-by-reference in their entirety. Many of the bearings have a structure similar to that shown in U.S. Pat. No. 4,144,963 (which is herein incorporated-by-reference in its entirety) that describes a plurality of anti-friction bearings made of synthetic thermoplastic resin such as Teflon®, Delrin®, polyethylene, etc., or other suitable material having a low coefficient of friction. Each bearing is substantially U-shape in cross-section, having a top wall and laterally-resilient side walls to overlap the top and sides of a guide beam. Each of the side walls is provided with a pair of downwardly and inwardly extending legs such that, when in position, the legs are positioned inwardly under the opposite sides of the guide beam to secure the bearing against vertical and longitudinal displacement. Bearings, however, can be problematic for many reasons including, but not limited to that they can slip or become worn, they require a large amount of labor to install, they require relatively close tolerances for fitting between the subdeck and slats, they allow road debris such as dust and salt to become entrapped between the deck and the bearing thus increasing wear of the slats, they add weight, and they are expensive to replace.
Live floor conveyors are often used to convey particulate matter. Sometimes it is undesirable to allow the particulate matter to escape the live floor conveyor. For example, shredded confidential paper can not be allowed to escape for legal reasons. Other types of loads such as feeds and fertilizers should not be allowed to filter through the conveyors and onto the ground while the system is in the operating mode. The filtering of chicken feed, for example, to the ground attracts wild birds which in turn can bring disease to flocks of young chickens and other fowl. U.S. Pat. No. 4,727,978 (which is herein incorporated-by-reference in its entirety) is a reciprocating conveyor formed of at least one group of slats of inverted U-shape that are spaced apart laterally. The downward side sections of adjacent slats are positioned within an elongated trough into which the particulate matter is deposited. It should be noted that because the troughs do not support or guide the slats, additional structures such as tubular support members and bearing members must be used.
U.S. Pat. No. 4,611,708 (which is herein incorporated-by-reference in its entirety) is directed to a system that has floor members (slats) that are supported on guide beams with bearing means between the floor members and the guide beams. Channels are formed between the guide beams. Matter such as refrigerated air, small particles of ice, water, and garbage are allowed to enter into the channel space. One problem with this conveyor is that large particles can collect in the channel and remain in the channel after the load has been unloaded. When the particles are confidential documents this problem is not tolerable. When various cargos are being hauled with the same conveyor it is undesirable to mix the cargos. Mixing would occur with this open channel floor. Another problem is that the position of the slat on the guide beam is not very stable. The wide slat is supported only along the length of its center and, therefore, any heavy object sitting offset on the slat can cause the slat to tip on its side and cause uneven wear.
U.S. Pat. No. 5,727,672 (which is herein incorporated-by-reference in its entirety) is directed to a system that uses four primary components: pultruded conveyor slats, bearings, guide members, and support members. The slats have downwardly directed lower sections that grip the guide members. The slats also have wing portions that are supported by the bearings that are, in turn, supported by the support members. The bearings also act as a seal to prevent particulate matter from escaping. If, however, particulate matter gets past the bearing seal, it will escape the conveyor system. Since the pathway for material to escape has a horizontal portion and a downward portion it is natural for material to leak. In other words, there is little resistance to leakage except for the weight of the load on the slat on the seal. Also, there is little to prevent material from entering the sliding contact area between the bearing and the slat. When particles enter this joint they reduce the effectiveness of the bearing and cause premature wear.
U.S. Pat. No. 6,257,396 (which is herein incorporated-by-reference in its entirety) is directed to a system that uses three primary components: slats, bearing strips (having a longitudinal groove on the top surface thereof), and longitudinal beams. The longitudinal beams are shaped like channels. The bearing strips are supported on the longitudinal beams, but completely enclose the interior of the channels. The slats are longitudinally supported on two adjacent bearing strips and longitudinal beams. This reference states that particulate matter that filters between the edges of the adjoining slats falls into the grooves in the bearing strips and is cleared away during the conveying process and/or routine maintenance. If, however, particulate matter gets past the bearing strip, it will escape the conveyor system. In addition, the pathway for material to escape the cargo area and enter the contact area between the slat and the bearing is down and horizontal. There is little resistance to prevent material from entering the sliding contact area and thereby cause greater resistance to the sliding motion. Finally, the slat must have a stiff cross-section to resist buckling since the joint between the subdeck and the deck is very loose.
U.S. Pat. No. 6,513,648 (which is herein incorporated-by-reference in its entirety) is directed to a system that uses three primary components: elongated subdeck sections (which are joined together by liquid-tight seals) with upwardly projecting bearing supports, elongated bearings that wrap around the upwardly projecting bearing supports, and deck slats. If this system is functioning properly, it can be extremely effective and even liquid tight. However, if the seals fail or are not installed properly, there may be at least some places where particulate matter can escape from the conveyor system. In addition, the pathway for material to escape the cargo area and enter the contact area between the slat and the bearing is down and horizontal. There is little resistance to prevent material from entering the sliding contact area and thereby cause greater resistance to the sliding motion. The increased friction also occasionally causes the bearing to slide off the bearing posts.